In the past two months, I've continued along the lines suggested by the previous post, partly restringing the back 8' register in the lower regions and voicing the whole instrument down a bit. As was the case for the front 8', this has changed things for the better. Both rows of jacks now play well and repeat reliably.
With the overall strength of voicing altered, I tweaked the separation between both rows of jacks by revisiting the jack end screws. I ended up giving each another half-turn, so the back 8' now sits beneath the strings by the equivalent of 4 half-turns, and the front 8' by 8 half-turns. This gives a tiny bit more slack to the mechanism.
It's important to recognize that the primary means of controlling the interaction of the two registers when both are turned on is by means of consistent voicing, and not indiscriminate cranking of these end screws. The screws are meant to adjust how long it takes for the plectrum to rise up and contact the string from beneath. There may be small differences here and there due to the quill angle in the tongue, which are a result of the quill mortise punching process, and an extra half-turn or two of the end screws can correct for this, but that's the extent of their usefulness.
Showing posts with label plectrum. Show all posts
Showing posts with label plectrum. Show all posts
Thursday, December 31, 2009
Monday, August 31, 2009
Voicing
Voicing, in the context of harpsichord-making, refers to the cutting of plectra (also known as quills) in a manner that draws forth a musically enjoyable sound from the instrument and feels controllable to the performer's fingers.
The same term is also used to describe the adjustment of organ pipes after manufacture. Unlike organ voicing, however, the voicing of harpsichord plectra cannot fundamentally transform the sound of the instrument. The tone is largely determined by various construction factors and the stringing materials, not by how plectra are cut. Volume and touch can be affected, along with the degree of shrillness, but not much more.
Historically, raven and goose feathers were the preferred materials for quill. Today, real quills are still used by some makers, while many others use Delrin or Celcon plectra. Both of these are hard, slippery plastics that have a long working life. They don't sound exactly like real quill, though they can get close if worked on by a knowledgeable voicer.
The process begins with ghosting, or setting the silences. Jacks are placed into all register slots, black delrin plectra are installed into all tongues, and the side-to-side position of the register is adjusted until the tongues are about 5 mm from the strings. The plectra are then trimmed from the tip until they just brush the strings when the jack is raised, without actually plucking in the normal manner, though in the bass they are allowed to weakly pluck the strings to adjust for the wire thickness. This process yields a consistent plectrum length of around 5 mm. As each quill is trimmed, the tip (as viewed from the side) is given a chisel-shaped profile to assist the backward tilt of the tongue when the jack descends.
Next, the register is advanced forward so that the plectra project past the strings by about one string diameter. This is the correct "on" position. The correct "off" position is set slightly behind the position at which the plectra ghost the strings.
With the register turned on, the tongue springs in each jack are adjusted so that the tongue tilts back as the jack descends. The severest test is to let the jack down extremely slowly: if the plectrum doesn't get hung up on the string, then the jack will work properly in every playing scenario. If the spring is too firm, stopping the tongue from tilting adequately, the tongue spring is bent back slightly and tested until the jack descends reliably.
Voicing can now begin. The intention is to produce plectra that pluck the strings consistently but not so strongly that the tone is harsh. To the fingers, the plectrum should be neither too firm nor too weak. A gradation in touch from bass to treble is required. The bass needs stronger quills because the string feels like it stretches somewhat before it gets plucked, due to the deeper plucking point in this region. In the treble, the short strings and close plucking point makes things feel stiff, so a weaker quill is needed.
This process can be expedited by using quills of differing thicknesses. Before ghosting, I experimented with 8 different quill thicknesses, discovering where it helped to change from one thickness to the next. I erred on the heavy side, since of course a heavy quill can be thinned to maker it weaker, but nothing can be done to strengthen a weak quill. Ultimately I used 6 different thicknesses, changing approximately every tritone to a thinner quill.
Voicing requires controlled cuts on the sides, arrises and underside of the quill, all of which thin the quill and reduce its stiffness. When done sensitively, the resistance of the quill as it raises the string seems to yield slightly just before the pluck, which I find feels quite controllable to my fingers.
The customary tools for voicing are shown below:
A set of wire cutters helps to trim excessively long plectra from the back. The hemostat acts like a set of pliers for installing and removing quills. Either a #11 scalpel blade (shown above) or a #11 Xacto knife blade are used for cutting the plectra. A voicing block—in this case the hard end-grain surface of an ebony block—acts as a little cutting board.
Once both registers received their preliminary voicing—a lengthy process that took two days of on and off work—the jack end screws were adjusted to locate the plectra a consistent distance below the strings. I first unscrewed each screw considerably, lengthening each jack to the point that the plectrum was actually above the string even with the jack fully lowered. Then I screwed back in until the plectrum just barely slipped under the string. At this point, I gave the rear row of jacks (the "back 8") 3 more half-turns, and the front row (the "front 8") 6 more half-turns. This difference separates the plucking instant between the two rows so that, if they are both turned on and played together, they won't pluck at exactly the same time. Otherwise the touch would be extremely heavy.
With these preliminaries out of the way, the instrument was played for several days and any discrepancies were corrected by replacing plectra, shaving down plectra, or adjusting the jack end screws further. These screws should not be cranked around much once they are set, but sometimes one or two more half-turns make a positive difference.
The same term is also used to describe the adjustment of organ pipes after manufacture. Unlike organ voicing, however, the voicing of harpsichord plectra cannot fundamentally transform the sound of the instrument. The tone is largely determined by various construction factors and the stringing materials, not by how plectra are cut. Volume and touch can be affected, along with the degree of shrillness, but not much more.
Historically, raven and goose feathers were the preferred materials for quill. Today, real quills are still used by some makers, while many others use Delrin or Celcon plectra. Both of these are hard, slippery plastics that have a long working life. They don't sound exactly like real quill, though they can get close if worked on by a knowledgeable voicer.
The process begins with ghosting, or setting the silences. Jacks are placed into all register slots, black delrin plectra are installed into all tongues, and the side-to-side position of the register is adjusted until the tongues are about 5 mm from the strings. The plectra are then trimmed from the tip until they just brush the strings when the jack is raised, without actually plucking in the normal manner, though in the bass they are allowed to weakly pluck the strings to adjust for the wire thickness. This process yields a consistent plectrum length of around 5 mm. As each quill is trimmed, the tip (as viewed from the side) is given a chisel-shaped profile to assist the backward tilt of the tongue when the jack descends.
Next, the register is advanced forward so that the plectra project past the strings by about one string diameter. This is the correct "on" position. The correct "off" position is set slightly behind the position at which the plectra ghost the strings.
With the register turned on, the tongue springs in each jack are adjusted so that the tongue tilts back as the jack descends. The severest test is to let the jack down extremely slowly: if the plectrum doesn't get hung up on the string, then the jack will work properly in every playing scenario. If the spring is too firm, stopping the tongue from tilting adequately, the tongue spring is bent back slightly and tested until the jack descends reliably.
Voicing can now begin. The intention is to produce plectra that pluck the strings consistently but not so strongly that the tone is harsh. To the fingers, the plectrum should be neither too firm nor too weak. A gradation in touch from bass to treble is required. The bass needs stronger quills because the string feels like it stretches somewhat before it gets plucked, due to the deeper plucking point in this region. In the treble, the short strings and close plucking point makes things feel stiff, so a weaker quill is needed.
This process can be expedited by using quills of differing thicknesses. Before ghosting, I experimented with 8 different quill thicknesses, discovering where it helped to change from one thickness to the next. I erred on the heavy side, since of course a heavy quill can be thinned to maker it weaker, but nothing can be done to strengthen a weak quill. Ultimately I used 6 different thicknesses, changing approximately every tritone to a thinner quill.
Voicing requires controlled cuts on the sides, arrises and underside of the quill, all of which thin the quill and reduce its stiffness. When done sensitively, the resistance of the quill as it raises the string seems to yield slightly just before the pluck, which I find feels quite controllable to my fingers.
The customary tools for voicing are shown below:
A set of wire cutters helps to trim excessively long plectra from the back. The hemostat acts like a set of pliers for installing and removing quills. Either a #11 scalpel blade (shown above) or a #11 Xacto knife blade are used for cutting the plectra. A voicing block—in this case the hard end-grain surface of an ebony block—acts as a little cutting board.
Once both registers received their preliminary voicing—a lengthy process that took two days of on and off work—the jack end screws were adjusted to locate the plectra a consistent distance below the strings. I first unscrewed each screw considerably, lengthening each jack to the point that the plectrum was actually above the string even with the jack fully lowered. Then I screwed back in until the plectrum just barely slipped under the string. At this point, I gave the rear row of jacks (the "back 8") 3 more half-turns, and the front row (the "front 8") 6 more half-turns. This difference separates the plucking instant between the two rows so that, if they are both turned on and played together, they won't pluck at exactly the same time. Otherwise the touch would be extremely heavy.
With these preliminaries out of the way, the instrument was played for several days and any discrepancies were corrected by replacing plectra, shaving down plectra, or adjusting the jack end screws further. These screws should not be cranked around much once they are set, but sometimes one or two more half-turns make a positive difference.
Sunday, June 14, 2009
Punching the mortises
Each tongue has a little mortise which holds the plectrum that plucks the string. This mortise is made by punching a slot through the tongue from back to front.
The punching setup at the drill press is a reasonably simple affair:
Using the drill press gives me a handle to press the punch down with, and also maintains a consistent punching angle. Jacks tend to work better if the plectra angle upwards slightly, so I tilted the table 5 degrees.
The punch itself is a 2.0 × 0.4 mm micro-screwdriver blade held in a small drill chuck. The tip passes through the slot in the maple block, which acts as a hold-down for the tongue and helps to pry the punch off as it is withdrawn. Underneath the tongue a slice of end-grain maple acts as a firm surface to work on. I set up the jig to punch the slot 9.5 mm from the top of the tongue, exactly at the point where the tongues were previously grooved across the back.
Before and after pictures showing how the tongue is punched:
This setup worked quite well in punching the mortises. The trick is to make sure the punch is not significantly wedge-shaped in profile, or it will split the tongue. I'm pleased to say that not a single tongue out of more than 130 was lost this way.
The one minor flaw I discovered is that the punching operation produces a bubble of compressed wood on the front face of the tongue that I had to slice off with a chisel to reopen the mortise. My end-grain maple wasn't a hard enough surface to prevent this from happening. Perhaps it would have been better to use a piece of metal with a small slot in it to allow the screwdriver tip to pass right through the front of the tongue. Otherwise, this was a creditable first attempt.
The punching setup at the drill press is a reasonably simple affair:
Using the drill press gives me a handle to press the punch down with, and also maintains a consistent punching angle. Jacks tend to work better if the plectra angle upwards slightly, so I tilted the table 5 degrees.
The punch itself is a 2.0 × 0.4 mm micro-screwdriver blade held in a small drill chuck. The tip passes through the slot in the maple block, which acts as a hold-down for the tongue and helps to pry the punch off as it is withdrawn. Underneath the tongue a slice of end-grain maple acts as a firm surface to work on. I set up the jig to punch the slot 9.5 mm from the top of the tongue, exactly at the point where the tongues were previously grooved across the back.
Before and after pictures showing how the tongue is punched:
This setup worked quite well in punching the mortises. The trick is to make sure the punch is not significantly wedge-shaped in profile, or it will split the tongue. I'm pleased to say that not a single tongue out of more than 130 was lost this way.
The one minor flaw I discovered is that the punching operation produces a bubble of compressed wood on the front face of the tongue that I had to slice off with a chisel to reopen the mortise. My end-grain maple wasn't a hard enough surface to prevent this from happening. Perhaps it would have been better to use a piece of metal with a small slot in it to allow the screwdriver tip to pass right through the front of the tongue. Otherwise, this was a creditable first attempt.
Friday, June 5, 2009
Jack tongues
The tongue fits in the slot routed into the jack body and is kept in place by a small axle pin. A mortise is punched completely through to receive the plectrum.
Holly, a fine-grained wood, was historically one of the commonly used materials for the tongues. I'm sticking with tradition and will be using the sheet of holly seen in the photo that also shows the resawed walnut the jack bodies came from.
First I cross-cut strips 28 mm wide from the sheet. Each strip can be imagined as a bunch of tongues attached together side-by-side, hence the need to cut across the grain. My tongue slot is 30 mm, but I feel the tongues should stop slightly short of the top of the slot so that the tongue doesn't absorb any of the repeated impacts of the jack hitting the jackrail over and over. That might bend the axle or break the tongue. The tongues will be slightly inset from the front face of the jack, instead of being flush.
Once the strips were made, I chamfered one edge at 25 degrees with a chamfering router bit. This edge will rest against the angled bottom of the tongue slot; the difference in angles between the two (25 degrees versus about 40 degrees) gives me some clearance that will be explained shortly.
Next, I needed to mark where the plectrum mortise would be. On some historical jacks, a small groove across the back of the tongue shows the location, and also thins the tongue to facilitate punching the mortise successfully.
I'm placing my mortise 9.5 mm from the top. That location was marked by making a 1/32" groove with a special small router bit. The groove is about 1 mm deep, reducing the thickness that needs to be punched through from 3 mm to 2 mm:
Individual tongues were sawn from these strips at the bandsaw. With a few strokes of sandpaper, the sawn edges were cleaned up.
A finished tongue:
I punched a test mortise on this one, and luckily it worked without splitting. More on making the mortises in the next post.
Holly, a fine-grained wood, was historically one of the commonly used materials for the tongues. I'm sticking with tradition and will be using the sheet of holly seen in the photo that also shows the resawed walnut the jack bodies came from.
First I cross-cut strips 28 mm wide from the sheet. Each strip can be imagined as a bunch of tongues attached together side-by-side, hence the need to cut across the grain. My tongue slot is 30 mm, but I feel the tongues should stop slightly short of the top of the slot so that the tongue doesn't absorb any of the repeated impacts of the jack hitting the jackrail over and over. That might bend the axle or break the tongue. The tongues will be slightly inset from the front face of the jack, instead of being flush.
Once the strips were made, I chamfered one edge at 25 degrees with a chamfering router bit. This edge will rest against the angled bottom of the tongue slot; the difference in angles between the two (25 degrees versus about 40 degrees) gives me some clearance that will be explained shortly.
Next, I needed to mark where the plectrum mortise would be. On some historical jacks, a small groove across the back of the tongue shows the location, and also thins the tongue to facilitate punching the mortise successfully.
I'm placing my mortise 9.5 mm from the top. That location was marked by making a 1/32" groove with a special small router bit. The groove is about 1 mm deep, reducing the thickness that needs to be punched through from 3 mm to 2 mm:
Individual tongues were sawn from these strips at the bandsaw. With a few strokes of sandpaper, the sawn edges were cleaned up.
A finished tongue:
I punched a test mortise on this one, and luckily it worked without splitting. More on making the mortises in the next post.
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